I know Elk are pretty big animals but do you really think that a 338 ultra-mag is what you need? Elk will go down to a .270 if you place it right, heck I've heard of them falling to a 30-30 if the shooter knows what he's doing.
I think that big guns are pretty cool too but you'd probably be better off with a good .308 or 30-06. You will probably shoot much better with one as the ammo is cheap enough to get a lot of practice and the recoil/muzzle blast won't make you flinch. That big 338 ultra with a muzzle brake is going to deafen the crap out of you and slap your face every time you pull the trigger. Go with the gun you shoot best, not the one that makes the biggest boom.